Post-mold cooling apparatus

ABSTRACT

The present invention relates to an improved method and apparatus for injection molding and cooling molded articles such as preforms so as to avoid crystallinity. The apparatus and method make use of a take-off plate for removing articles from a mold, which plate may include heat transfer devices for cooling exterior surfaces of the molded articles or preforms, and a system for cooling in a controlled manner interior surfaces of the molded articles or preforms.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional Application of U.S. patent applicationSer. No. 09/613,947, filed Jul. 11, 2000 now U.S. Pat. No. 6,475,422,incorporated herein by reference, which is a Divisional application ofSer. No. 09/119,256, filed Jul. 20, 1998, now U.S. Pat. No. 6,171,541,which claims benefit from Provisional Application Ser. No. 60/080,085,filed Mar. 31, 1998.

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for molding andcooling plastic molded articles such as preforms made of single ormultiple materials such as plastic resins. In particular, the inventionteaches a rapid injection molding process where the molded articles,such as PET preforms, are ejected from the mold before the cooling stepis complete. This is possible as a result of the utilization of a newpost-mold cooling process and apparatus where the preforms are cooledinternally by convection heat transfer, after being removed from themold and retained outside the mold area. The present invention alsoteaches additional external cooling, done through either convection orconduction heat transfer, which may take place at least partiallysimultaneously with the internal cooling.

Proper cooling of molded articles represents a very critical aspect ofthe injection molding process because it affects the quality of thearticle and impacts the overall injection cycle time. This becomes evenmore critical in applications where semicrystalline resins are used,such as the injection molding of PET preforms. After injection, the PETresin remains in the mold cavity space for cooling for a sufficientperiod of time to prevent formation of crystalline portions and to allowthe preform to solidify before being ejected.

Two things typically happen if a preform is rapidly ejected from a moldin order to reduce the cycle time of the injection process. The first isthat the preform is not uniformly cooled. In most instances, the bottomportion opposed to the mold gate is crystallized. The amount of heataccumulated in the walls of the preforms during the injection processwill still be high enough to induce post molding crystallinityespecially in the gate area of the preform. The gate area is a verycritical spot because cooling of the mold in this portion is noteffective enough and also because the resin in the mold cavity space isstill in contact with the hot stem of the hot runner injection nozzle.If this area of a preform remains crystalline above a certain size anddepth, this will weaken the quality of a blown article. The second isthat the preform will be too soft and thus can be deformed during thenext handling steps. Another critical area of a preform is the neckfinish portion which in many instances has a thicker wall and thusretains more heat than the other portions. This neck portion needsaggressive post-mold cooling to prevent it from becoming crystallized.Also aggressive cooling tends to make the neck solid enough to sustainfurther manipulations.

Many attempts have been made in the past to improve the coolingefficiency of PET injection molding systems, but they have not resultedin a significant improvement in the quality of the molded preforms or asubstantial reduction of the cycle time. Reference is made in thisregard to the U.S. Pat. No. 4,382,905 to Valyi which discloses aninjection molding method where the molded preform is transferred to afirst tempering mold for a first cooling step and then to a secondtempering mold for a final cooling step. Both tempering molds aresimilar to the injection mold and have internal means for cooling theirwalls that make contact with the preform during the cooling process.Valyi '905 does not teach the provision of cooling devices located onthe means for transferring the preforms from the molding area oradditional cooling devices that circulate a fluid coolant inside themolded parison.

U.S. Pat. No. 4,592,719 to Bellehache discloses an injection moldingmethod for fabricating PET preforms where molded preforms are removedfrom the injection cores by a first movable device comprising vacuumsucking devices for holding the preforms and also comprising airabsorption (convection) cooling of the outer surface of the preform. Asecond cooling device is used by Bellehache '719 in conjunction with asecond movable device to further cool the inside of the preforms also byair absorption. See FIG. 22 herein. Bellehache '719 does not teach coldair blowing inside a preform which has a significantly higher coolingeffect with respect to sucking or absorbing ambient air and also doesnot teach cooling means by conduction heat transfer located in intimatecontact with the preforms wall and air blow means directed to the domeportion of the preforms. Bellehache suffers from a number ofdeficiencies including less cooling efficiency, less uniformity, longercooling time, high potential for preform deformation.

U.S. Pat. Nos. 5,176,871 and 5,232,715 show a preform cooling method andapparatus. The molded preform is retained by the injection molding coreoutside the mold area. The mold core is cooled by a coolant that doesnot make contact with the molded preform. A cooling tube larger than thepreform is placed around the preform to blow cooling air around thepreform. The principal problem with the apparatus and method shown inthese patents is that the preform is retained in the mold core and thissignificantly increases the cycle time. Also internal cooling is notachieved by direct contact between coolant and the preform.

Further reference is made to U.S. Pat. Nos. 5,114,327, 5,232,641,5,338,172, and 5,514,309 that teach a preform internal cooling methodusing a liquid coolant. Preforms ejected from a mold are transferred toa preform carrier having vacuum means to retain the preforms in placewithout making contact with the preforms' external wall. The preformscarrier however does not have any cooling devices. Cooling cores arefurther introduced inside the preforms retained by the carrier and acooling fluid is blown inside the preforms to cool them. The coolant isfurther removed by the same vacuum means that retain the preforms fromthe chamber surrounding the preforms. These patents do not teach blowingcold air inside a preform where the air freely leaves the preform aftercooling. These patents also do not teach simultaneous cooling of thepreforms internally and externally or a preform carrier having coolingmeans. See FIG. 21 shown herein.

Further reference is made to Japanese Pat. Discl. 7-171888 which teachesa preform cooling apparatus and method. A molded preforms robot carrieris used to transfer the preforms to a cooling station. The robotincludes external cooling of the preforms walls by conduction thermaltransfer using a water coolant. The cooling station comprises a firstmovable transfer robot that has a rotary hand portion including vacuummeans for holding the preforms and also external cooling of the preformswalls by conduction thermal transfer. The molded preforms aretransferred from the robot carrier to the hand portion. The hand portionis moved from position A to position B where it is rotated by 90° inorder to transfer the preforms (cooled so far only at the exterior) to acooling tool. The cooling tool has means to hold the performs, devicesto cool the inside of the preforms by blowing air and devices to coolthe outside of the preforms by either blowing air or water cooling. Theinternal cooling which is employed is shown in FIGS. 19 and 20 herein.This patent does not teach a cooling method where internal and externalcooling are performed as soon as possible from the moment the preformsare ejected from the mold and into a carrier plate. It also does notteach simultaneous internal and external cooling of the preforms whilethey are retained by the movable robot carrier. Therefore, this coolingmethod is not fast enough and does not prevent crystallinity formationoutside the mold.

FIGS. 19 and 20 show known methods of internally cooling preforms wherea cooling device is located outside the preform and is used to blow coolair inside the preform. Because the air nozzle is located outside thepreform, the incoming cold air flow will inevitably interfere and mix atleast partially with the outcoming warm flow. This will significantlyreduce the cooling efficiency. If the cooling device is on the same axiswith the preform, the approach of FIG. 19 is ineffective because thereis no air circulation in the preform. If the cooling device is laterallyshifted as in FIG. 20, internal air circulation is achieved, but this isstill ineffective because one side of the preform is better and fastercooled than the other. The coolant has a quasi-divergent flow profilewith a non-symmetrical profile. This profile is very ineffective and itdoes not allow to concentrate the cooling fluid/gas towards the spruegate or dome portion.

SUMMARY OF THE INVENTION

It is a principal object of the present invention to provide a methodand apparatus for producing preforms which have improved coolingefficiency.

It is a further object of the present invention to provide a method andapparatus as above which produce preforms having improved quality.

It is yet another object of the present invention to provide a methodand apparatus as above which reduce overall cycle time.

The foregoing objects are obtained by the apparatus and method of thepresent invention.

In one embodiment, the innovative molding and cooling method of thepresent invention includes removing the preforms from the mold beforethe preforms are fully cooled inside the mold, i.e. the preforms retaina certain amount of heat that may potentially crystallize the sprue gateportion, the neck finish or the entire preform; retaining the preformsoutside the molding area; and internally cooling the preforms byconvection heat transfer so that crystallization does not occur in anyof those regions.

In another embodiment, the innovative molding and cooling method of thepresent invention comprises removing the preforms from the mold beforethe preforms are fully cooled inside the mold, i.e. they still reatin acertain amount of heat that may potentially crustallize the sprue gateportion, the neck finish portion or the entire preform; retaining thepreforms outside the molding area; internally cooling the preforms byconvection heat transfer so that crystalliztion does not occur in any ofthe aforementioned regions, said cooling step comprising placing thecoolant in direct contact with the preform; and externally cooling thepreforms by convection heat transfer so the crystallization does notoccur in any of the aforementioned regions. The external cooling stepmay be performed simultaneously, at least partially simultaneously, orsequentially, with respect to the internal cooling step.

In yet another embodiment, the innovative molding and cooling method ofthe present invention comprises removing the preforms from the moldbefore the preforms are fully cooled inside the mold, i.e. they stillretain a certain amount of heat that may potentially crystallize thesprue gate portion, the neck finish portion, or the entire preform;retaining the preforms outside the molding area; internally cooling thepreforms by convection heat transfer so that crystallization does notoccur in any of those regions, said internal cooling step comprisingplacing the coolant in direct contact with the preform; and externallycooling the preform by conduction heat transfer so that crystallizationdoes not occur in any of the aforementioned regions. The externalcooling step may be performed simultaneously, at least partiallysimultaneously, or sequentially with respect to the internal cooling.

In each of these embodiments, the preforms are ejected from the mold andare retained external to the mold by means independent of the mold suchas for example a movable take-off plate. Such independent retentionmeans may retain one batch of molded preforms or several batches ofpreforms simultaneously. When several batches are held by theindependent means, the batches will have different temperatures becausethey were molded at different times. According to the present invention,the molded preforms will be cooled in different sequences internally andexternally using the cooling method of the present invention. In eachembodiment of the present invention, internal cooling is done usingmeans, such as cooling pins, that enter at least partially inside thepreform and circulate coolant therein. cooling is preferentially done bya quasi-symmetrical flow of coolant delivered inside the preform thatcan be directed towards the portions of the preforms that need morecooling than the others, such as the sprue gate and the neck finish. Ina preferred embodiment of the present invention, the coolant is directedtoward the bottom or dome portion of the preform so as to create anannular flow of coolant.

In certain embodiments of the present invention, the innovative internalcooling of the preforms is supplemented by external cooling that can bedone in several ways. For example, the external cooling can be done on atake out plate (single or multiple position) that has cooling meansoperative using either conductive (cooled water) or convection (air/gas)heat transfer. It also can be done on a take out plate (single ormultiple position) that does not have cooling means whereby the preformsare only partially in contact with their holders. In this way, coolinggas/air can be delivered by an independent cooling device to directlytouch the outer surface of the preforms.

Yet in another embodiment, the preforms are retained in a take-out platethat does not have any cooling means and are solely cooled internally bythe new cooling pins of the present invention.

The innovative cooling approach of the present invention in oneembodiment may be achieved by removing the preforms or molded articlesfrom the mold, holding the preforms or molded articles in a robottake-off-plate having a system for cooling the exterior surfaces of thepreforms or molded articles, and thereafter engaging cooling meansinside the preform or molded article to effect simultaneous cooling ofthe exterior and interior surfaces. According to the present invention,an additional cooling step is introduced whereby the temperature of thepreform is reduced using heat transfer by convection, such as bycirculating a cooling gas inside the preform.

The method and apparatus according to the present invention, aspreviously discussed, can be advantageously used to preventcrystallization in the most critical areas of preforms, namely thebottom part or the dome portion where the sprue gate is located and theneck portion. Further, the cooling method and apparatus of the presentinvention can be integrated into an injection-blow molding machine wherethe cooled preforms with no crystallinity are further temperatureconditioned and blown into bottles.

In accordance with one aspect of the present invention, a method forpreventing crystallization in an injection molded preform by enhancedout of the mold cooling comprises injecting a molten material into amold formed by two mold halves or plates which in a mold open positionare spaced apart so as to define a molding area; cooling the moltenmaterial while in the mold cavity space formed by the mold halves up toa temperature substantially close to the crystal-glass transitiontemperature of the molten material so that the molded article can bemechanically handled outside the mold without suffering any geometricaldeformation; opening the mold halves by a distance sufficient to allow amolded article carrier to be moved between the two mold halves; ejectingthe molded articles from the mold and transferring them to the movablecarrier; cooling the molded articles while they are in the movablecarrier by heat transfer conduction to reduce crystallinity whereby thecoolant is blown air; and further internally cooling the molded articlesby convection heat transfer until each molded article is substantiallyfree of any crystallized portion. The same method can be implementedusing a movable carrier including convective heat transfer means forexternal cooling.

In accordance with one aspect of the present invention, the apparatusfor forming a de-crystallized, injection molded article comprises a moldhaving two mold halves which can be moved between a mold closed positionand a mold open position; means for injecting molten material into themold while the mold halves are in the mold closed position; means forcooling the molten material in the cavity space formed by the moldhalves up to a temperature substantially close the crystal-glasstransition temperature of the molten material so that the molded articlecan be mechanically handled outside the mold without suffering anygeometrical deformation; means for opening the mold so that the moldhalves are spaced apart a distance sufficient to allow a molded articlecarrier to be moved in between the two mold haves; means for ejectingthe molded articles from the mold; means for transferring the moldedarticles to the movable carrier; said carrier having means for holdingthe preforms and for cooling the molded articles by heat transferconduction to reduce crystallinity; and means for further internallycooling the molded articles by convection heat transfer until eachmolded article, preferably the entire article, is substantially free ofany crystallized portion, particularly in the mold gate area. The samemethod can be implemented using a movable carrier with conductive heattransfer means for external cooling.

As used herein, the terms “take-off plate”, “take-out plate” and “end ofarm tool” are used interchangeably and refer to the same structure(s).

Other details of the method and apparatus of the present invention, aswell as other objects and advantages attendant thereto, are set forth inthe following detailed description and the accompanying drawings inwhich like reference numerals depict like elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the preform temperature vs. time during andafter the injection step;

FIG. 2 is a schematic representation of a preform in the mold;

FIGS. 3(a) and 3(b) show the temperature gradient across the walls of amolded preform during cooling;

FIG. 3 c shows the temperature profile along the preform walls.

FIG. 4 is a sectional view showing a prior art injection mold;

FIG. 5 is a sectional view showing a movable robot including anend-of-arm-tool (EOAT) device placed in the molding area between thestationary and movable mold plates;

FIGS. 6(a) and 6(b) are side views showing an embodiment of the presentinvention including a robot take-off-plate (or end of arm tool, EOAT)and a frame holding cooling pins;

FIGS. 6(c) and 6(d) are front views of the embodiment of FIGS. 6(a) and6(b);

FIGS. 7(a)-7(d) shows the frame and the cooling pins according to afirst embodiment of the present invention;

FIGS. 8(a)-(g) shows several cooling pin designs according to thepresent invention;

FIGS. 9(a) and 9(b) illustrate a more detailed view of the cooling pinsaccording to two embodiments of the present invention;

FIG. 10(a) shows a preform having crystallized zones as they aregenerated in prior art methods;

FIG. 10(b) shows a preform without crystallized zones as it resultsafter the method of the present invention;

FIGS. 11(a)-11(l) show another embodiment of the frame and cooling pinsaccording to the present invention;

FIG. 12 is a sectional view of a system wherein air cooling channels areincorporated into the mold halves;

FIGS. 13(a) and 13(b) are side views of another embodiment of thecooling system of the present invention;

FIG. 14 is a top view of an injection molding system having anotherembodiment of the cooling system of the present invention;

FIG. 15 is a sectional view of yet another embodiment of the coolingsystem of the present invention showing the mechanism for cooling theinterior of the molded articles attached to the take-off-plate;

FIG. 16 illustrates an embodiment of the present invention wherein atake-off plate with no cooling means is used to remove the moldedpreforms from the molding area;

FIG. 17 illustrates the construction of an alternative cooling pin inaccordance with the present invention;

FIGS. 18(a) and (b) illustrate the construction of yet anotheralternative cooling pin in accordance with the present invention;

FIGS. 19 and 20 illustrate prior art methods for cooling the interior ofa preform;

FIG. 21 illustrates another prior art system for cooling the interiorand the exterior of a preform;

FIG. 22 illustrates a prior art system using the sucking of ambient airto cool a preform; and

FIG. 23 illustrates an alternative frame construction with cooling pinson multiple surfaces of the frame.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, FIG. 1 is a graph showing the evolutionof preform temperature vs. time during and after the injection step.FIG. 2 is a schematic representation of a preform while it is in themold. As can be seen from this figure, cooling while in the mold istypically effected by cooling tubes 12 and 14 positioned within the moldcavity 16 and the mold core portions 18 respectively. As a result,cooling is effected from both sides of the preform 11. Further, as shownin FIG. 2, the mold cavity plate 16 typically has a gate region 20 atwhich the bottom part or the dome portion 22 of the preform 11 isformed. The preform has a neck finish portion 13 which sometimes has athick wall which is difficult to cool to prevent crystallinity.

FIGS. 3(a) and 3(b) show the temperature gradient across the walls of amolded preform during cooling. FIG. 3(a) shows the temperature gradientinside the mold, while FIG. 3(b) shows the temperature gradient outsidethe mold. FIG. 3(c) shows the temperature profile along the preformwalls. The temperature spike represents the temperature in the dome orsprue gate portion of the preform.

Referring now to FIG. 4, an injection mold is provided which includes astationary mold half or plate 32 having an array of mold cavities 34 anda movable mold half or plate 36 having an array of mold cores 38. Themold cavity plate 32 is in fluid communication with a manifold plate(not shown) that receives molten material from an injection unit (notshown) of an injection molding machine. The mold cavities 34 receive themolten material from hot runner nozzles (not shown), such as for examplea valve gated nozzle (not shown), through mold cavity gates 40. The moldcavities are each surrounded by cooling means 42 for cooling the moltenmaterial in the cavity space formed by the mold core 38 and the moldcavity 34 when the mold plates 32 and 36 are in a mold closed position.The cooling means 42 are preferably formed by cooling channels embeddedwithin the mold plate 32 for conducting a cooling fluid. As previouslydiscussed, the mold cores 38 and the mold cavities 34 form in the moldclosed position a plurality of mold cavity spaces (not shown) that arefilled with molten material through the mold gates 40 during theinjection step. The mold cores 38 also include means 44 for cooling themolten material in the cavity space. The cooling means 44 preferablycomprise a cooling tube within each mold core. The mold core plate 36further includes an ejector plate 46 which is used to remove the moldedpreforms 48 from the mold cores 38. The operation of the ejector plate46 is well known in the prior art and does not form part of the presentinvention. In fact, the ejector plate 46 may comprise any suitableejector plate known in the art.

According to the current invention, any molten plastic, metal or ceramicmaterial can be injected into the mold cavity space and cooled into adesired article using the mold system of FIG. 4. In a preferredembodiment of the current invention, the molten material is PET and themolded article is a preform. According to the present invention however,the molded article can also be a preform made of more than one material,such as for example virgin PET, recycled PET and an appropriate barriermaterial such as for example EVOH.

As is known in the art, a preform is molded by closing the mold,injecting the molten material into the cavity space, initiating coolingof the cavity space, filling the cavity space, holding the moltenmaterial under pressure, performing final in-mold cooling, opening themold, ejecting the solidified articles or preforms from the cores andtransferring the articles or preforms to a take-off plate.

According to the present invention, in order to reduce the overall cycletime, the residence time of the preform in the mold has to be minimal sothat the mold is able to produce batches of preforms as fast aspossible. The problem with a reduced residence time in the mold is thatthe cooling time has to be reduced, but in such a manner that the moldedarticles or preforms are solid enough to withstand all the subsequenthandling steps without deformation. A reduced cooling time is aproblematic option because the articles or preforms are not sufficientlyand uniformly cooled by the cooling means 42 and 44. The amount of heatretained by the article or preform after being cooled inside the moldfor a reduced time and immediately after opening the mold is verysignificant and depends on the thickness of the molded article orpreform. This internal heat has the potential to generate crystallizedportions at the sprue gate area or dome portion of the molded article orpreform, the neck finish portion of the molded article or preform, orthe entire preform. In order to prevent the crystallization of themolded article or preform, a very aggressive cooling method has to beused. During cooling, attention must be paid so as to control theshrinkage of the molded articles which can adversely affect their finaldimensions.

FIG. 5 illustrates one embodiment of a robot take-off plate 60 which canbe used in the cooling method of the present invention. The take-offplate 60 includes a plurality of hollow holders or receptacles 62 whichcan be water cooled tubes. Typical take-off plates which may be used forthe take-off plate 60 are shown in U.S. Pat. No. 5,447,426 to Gessner etal. and in U.S. Reissue Pat. No. RE 33,237 to Delfer, III, both of whichare incorporated by reference herein. In operation, the mouth of aplurality of holders 62 are aligned with the mold cores 38 of the moldplate 36. Transfer of the molded articles 48 to the holders 62 iseffected by operation of the ejector plate 46. According to the presentinvention, the take-off plate 60 can be provided with a number ofholders 62 equal to the number of mold cores 38 or a larger number ofholders 62 such as a multiple of the number of mold cores, for examplethree or four times the number of mold cores. By having more holders 62than the number of cores 38, it is possible to retain some of the moldedarticles for a time longer that a single molding cycle and therebyincrease the cooling time while maintaining a high output of moldedarticles. The method of the present invention can be carried outirrespective of the relative number of molded articles retained by theholders 62. Nevertheless, in the preferred embodiment of the invention,the robot take-off plate 60 has a number of holders 62 which representthree times the number of cores 38. This means that the take-off plate60 does not always carry a number of preforms or molded articles equalto the number of holders 62. This also means that a single batch ofpreforms can be moved back more than once into the mold area between themold core and cavity plates to pick up other batches of molded articles,while being cooled by intimate contact between the hollow tubes 64within the take-off plate, which tubes 64 carry a cooling liquid such aswater, and the external wall of the preforms as shown in more detail inthe aforementioned U.S. Pat. No. 5,447,426. The heat transfer betweenthe tubes 64 and the hot molded articles released from the mold isperformed through conduction. More particularly, any solid materialincorporating any cooling means can be used and brought into intimatecontact with the exterior wall of the molded articles to cool the moldedarticles. By using a cooling system based on heat transfer throughconduction implemented through an intimate contact between the moldedarticle or preform and the cooling means, the shape of the article orpreform is maintained without deformations or scratches caused byhandling.

If desired, the conductive cooling means 64 employed in the take-offplate can be replaced by a convective heat transfer means. Any suitableconvective heat transfer means known in the art may be used with thetake-off plate 60 to effect cooling of the exterior surfaces of themolded articles or preforms carried by the take-off plate 60.

Referring now to FIGS. 6(a) and 6(b), an additional cooling device 70 isused in conjunction with the robot take-off plate 60 to enhance thepost-mold cooling efficiency by allowing simultaneous cooling of theinterior and exterior surfaces of the molded articles or preforms byconvective heat transfer and thus reduce the cycle time and improve thequality of the preforms. The additional cooling device 70 includes anarray of elongated cooling pins 74 whose role is to deliver a coolingfluid inside the molded articles held by the take-off plate 60. In apreferred embodiment of the present invention, the cooling fluid ismostly directed and delivered directly into the dome (sprue gate)portion 22 of the molded article or preform, which portion has thehighest chance to become crystalline due to the reduction of the coolingtime in the mold. The cooling fluid is introduced so as to create anannular flow pattern. According to the present invention, the coolingfluid could be any appropriate coolant, such as for example a liquid ora gas. In a preferred embodiment of the present invention, the coolingfluid is pressurized air delivered at through a channel 90 locatedinside the cooling pin 74. This aspect of the present invention is shownin more detail in FIG. 9(a).

FIG. 9(a) illustrates a cooling pin 74 in accordance with the presentinvention positioned within a preform or molded article 48 being cooled.In order to create an optimum flow of the cooling agent, the cooling pin74 is introduced deep inside the preform 48 so that the coolant canreach the dome or sprue gate portion 22. More than that, the cooling pin74 acts as an additional cooling core. The cooling pin 74 alsocontributes to the creation of an annular flow pattern which has ahigher cooling potential than other cooling flow patterns. Also by usingthe novel cooling pin 74, the incoming blown cold air and outcoming warmair are completely separated and thus prevents mixing of the two.

As shown in FIG. 9(a), the cooling pin 74 is positioned centrally withinthe preform or molded article, preferably so that the central axis 220of the cooling pin 74 is aligned with the central axis 222 of thepreform. As can be seen from this figure, the outer wall 224 of thecooling pin 74 in an upper region UP is spaced from the inner wall 226of the preform by a distance D. Additionally, the outlet nozzle 92 ofthe cooling pin 74 is spaced from the inner wall 228 of the dome portion22 by a distance d. In order to create the desired annular flow patternof cooling fluid, it is preferred that the ratio of d:D be within therange of about 1:1 to about 10:1. It is also highly desirable that theoutlet nozzle 92 of the cooling pin be formed by a divergent nozzleconstruction. While it is preferred to use a divergent nozzle for theoutlet 92, it is possible to form the outlet 92 from a straight wallednozzle construction.

Because cooling pin 74 goes deep inside the preform and behaves like acooling core as well, the pattern of outcoming warm air that freelyescapes from the preform has an annular shape.

While a preferred construction for the cooling pin has been shown inFIG. 9(a), as shown in FIGS. 8(a) through 8(g), 17 and 18, the coolingpins 74 can have various sizes and shapes to achieve various coolingeffects. For example, as shown in FIG. 8(a), the lower portion LP of thecooling pin may have a diameter D₂ which is different from the diameterD₁ of an upper portion UP of the pin. As shown in FIGS. 8(a) through8(c), the upper portion UP of the pins may have different shapes.Referring to FIG. 8(d), the cooling pin 74 may have lateral outlets 82for discharging a cooling fluid onto side walls of the molded articlewhere crystallinity may occur. As shown in FIG. 8(e), the cooling pin 74could have helical grooves 84 to obtain specialized cooling effects.Similarly in FIGS. 8(f) and 8(g), the cooling pin 74 could have aplurality of ribs 86 spaced about its periphery or a plurality ofcontact elements 88.

FIGS. 18 a and 18 b illustrate a cooling pin 74 having a plurality ofradial conduits 230 for delivering coolant on areas of the preform otherthan the dome portion 22 such as the neck finish portion or the bodyportion. The radial conduits 230 may be spaced along the length of thecooling pin so as to direct coolant against particular areas of apreform 48.

The cooling pins 74 can be made from any suitably thermally conductiveor thermally insulative material. If desired, as shown in FIG. 17, thecooling pin 74 may be made from a porous material 232 so that additionalcoolant can be spread in a very uniform manner on areas of a preformother than the dome or sprue gate portion 22.

In a preferred embodiment of the present invention, the design of thecooling pin 74 is intended to concentrate maximum cooling at the spruegate or dome portion 22 of the molded article 48 and thus aggressivelyfocus the cooling fluid to cool this region. In this way, moldedarticles such as preforms free of crystallized areas in the sprue gateor dome portion 22 can be formed.

An alternative pin construction with a cold air blowing system which canbe used in the apparatus of the present invention is illustrated in FIG.9(b). As shown therein, the pin 74 has a cold air blowing channel 90having an outlet 92 for directing cold air against the interior surfacesof the molded article 48, preferably the dome or sprue gate portion 22of the molded article. The channel 90 communicates with a source of coldair (not shown) via the inlet 94. The cooling pin 74 is further providedwith a vacuum channel 96 for removing the cooling air from the interiorof the molded article 48. The vacuum channel 96 may be connected to anydesired vacuum source (not shown). As can be seen in FIG. 9(b), thecooling pin 74 is mounted on a portion of a frame 98 by sliding pads100, which are used for pin self-alignment, and a fastening means suchas nut 102. The nut 102 can be secured to the element 104 which has anexterior threaded portion (not shown).

Referring now to FIGS. 6 and 7, the array of cooling pins 74 is mountedonto a cooling frame 98 which can be made of a lightweight material suchas aluminum. According to the present invention, the cooling frame 98can be operated in either a vertical or a horizontal position. In bothcases, the frame 98 is movable towards the take-off plate 60 when thetake-off plate 60 reaches its final out of mold position. Any suitablemeans known in the art may be used to move the frame 98 so as to advanceit at a high speed so that the cooling pins 74 can be immediatelyintroduced inside the molded article. In a preferred embodiment of thepresent invention, the frame 98 is moved using hydraulic cylinders 110.According to the present invention, the number of cooling pins 74 can bethe same or less than the number of receptacles 62 in the take-off plate60. According to the present invention, the take-off plate 60 isprovided with means for holding the molded articles or preforms 48within the receptacles 62 such as suction means (not shown), and withmeans for ejecting the preforms from the take-off plate. The holdingmeans and the ejection means may be those disclosed in theaforementioned U.S. Pat. No. 5,447,426 which has been incorporated byreference herein. As shown in FIGS. 6(c) and 6(d), the cooling frame 98is provided with a plurality of spaces 112. The spaces 112 allow finallycooled molded articles or preforms ejected from the take-off plate 60 tobe dropped onto a conveyor 114 for transportation away from the system.In a preferred embodiment of the present invention, the fully cooledpreforms 48 are dropped onto the conveyor 114 through the spaces 112 bylaterally shifting the cooling pins 74 relative to the receptacles 62holding the preforms that have to be ejected from the take-off-plate 60.This is the case when the cooling frame is in a horizontal position.When the cooling frame is in a vertical position, it does not interferewith the preforms dropped by the take-off-plate.

Referring now to FIGS. 7(a) and 7(b), a first array of cooling pins 74is illustrated. As can be seen in FIG. 7(b), the cooling pins 74 eachhave cooling air passageways 90 which communicate with a source ofcooling air (not shown) via the passageway 122. Incorporated into thepassageway 122 are a number of air valves 124 which can be used toregulate the flow of cooling air. In this way, variable amounts ofcooling air can be supplied to the cooling pins 74.

Referring now to FIG. 7(c), it is also possible to directly provide eachcooling pin 74 with air from a source of cooling fluid (not shown) via asimple passageway 126. Still further, as shown in FIG. 7(d), if desired,the passageway 126 could be connected to the fluid conduit 120 in eachof the cooling pins via a flexible conduit 128.

According to one embodiment of the present invention, the cooling pins74 enter the preforms retained by the take-off plate 60 in a few steps,and at each step the preforms that are molded at different times are atdifferent temperatures. In order to optimize the overall cooling stepand to avoid the waste of coolant, during the first step of cooling thepreforms are very hot and thus a maximum amount of cooling air isdelivered by the pins. In the second and the subsequent steps, theamount of cooling air directed by the pins engaging the first moldedpreforms is substantially less than the amount directed towards thenewly molded and hotter preforms. In order to further optimize thecooling process, any known suitable temperature sensors, such as athermocouples, can be used to measure the temperature of the preformsbefore and after cooling them so that adjustments of the cooling ratecan be done without interrupting the molding cycle. In a preferredembodiment, thermocouples (not shown) connected to some cooling controlmeans (not shown) are located in the take-off plate 60 adjacent to eachpreform. By monitoring the temperature of each preform, some adjustmentscan be made to the amount of cooling air delivered to all cooling pins74 or to some of the cooling pins 74. This may also compensate for anycooling inefficiencies or non-uniformity of the conduction cooling meanslocated in the take-off plate.

Referring now to FIGS. 10(a) and 10(b), FIG. 10(a) shows a preform 48,in sectional view, molded by a prior art system. As shown therein, thepreform 48 may have crystalline areas in four different zones includingthe dome portion 22 and the neck portion 13. FIG. 10(b) on the otherhand shows a preform 48, in section view, which has been manufacturedusing the system of the present invention. As shown therein, there areno areas of crystallinity.

Another embodiment of the present invention is shown in FIGS. 11(a)through 11(l) where the take-off plate 60′ is always maintained in avertical position during the entire molding cycle. This eliminates acomplicated motor and makes it lighter and thus faster to move in andout of the mold space formed between the mold halves or mold plates 32and 36. The cooling frame 98′ used in this system has an additionalfunction and an additional movement. First of all, the pins 74′ useblowing air to cool the molded articles or preforms and sucking air toextract the molded articles or preforms from the take-off plate 60′. Thepreforms are be held on the pins 74′ by the vacuum and removed from thetubes 62′ within the take-off plate 60′ during a back movement. Thecooling frame 98′ has a movement to approach and move back from thetake-off-plate 60′ and further has a rotation to move from a vertical toa horizontal position parallel to a conveyor 114′ to allow the preformsto be ejected from the pins 74′ by stopping the vacuum. According to thepresent invention, any suitable means known in the art can be used torotate the cooling frame 98′ with the pins 74′. According to a preferredembodiment of the invention shown in FIGS. 11(a) through 11(l), astationary cam 130 is used as a very simple means to convert thetranslation of the frame into a rotation so that the preforms held bythe cooling frame can be dropped onto a conveyor 114′. As shown in FIG.11(h), the cooling pins 74′ can engage the preforms by vacuum and removethem from the take-off plate 60′. Next the preforms are dropped from thepins 74′ onto a conveyor.

The operation of the innovative cooling apparatus of the presentinvention can be understood from FIGS. 6(a) through 6(d). After thein-mold cooling process which is shortened up to the point where thearticles or preforms reach a solidification status that prevents theirdeformation, the mold is opened and the take-off plate 60 is moved intothe molding area between the mold core plate 36 and the mold cavityplate 32. Relative movement between the mold core and mold cavity platesmay be performed in any manner known in the art using any suitable means(not shown) known in the art. After the take-off plate 60 reaches theout of the mold position, the cooling pins 74 are engaged with themolded articles for cooling, especially in the dome area 22 of eacharticle or preform.

While the take-off plate 60 has been described as having water cooledmeans for conduction cooling of the exterior surfaces of the preformswithin the holders 62, there are times when one would want to not startcooling of the exterior surfaces when the preforms are first placedwithin the take-off plate. To this end, means may be provided to controlcooling within the take-off plate so that such cooling does not startuntil after internal cooling of the preforms has begun and/or finished.For example, suitable valve means (not shown) may be incorporated intothe take-off plate to prevent flow of a cooling fluid until a desiredpoint in time. In this way, internal and external cooling of the preformmay be preformed simultaneously, at least partially simultaneously, orsequentially.

FIG. 16 illustrates another embodiment wherein a take-off plate 60″ withno cooling means is used to remove the molded preforms from the moldingarea. The take-off plate 60″ may have preform holders 62″ sufficient innumber to accommodate either a single batch or multiple batches ofpreforms. The preforms are retained by vacuum means (not shown) thatthrough the openings 240 suck on the sprue gate or dome portion 22 ofthe preforms 48. The preforms are also retained by the holders 62″ whichcan have any desired configuration that allows the preforms to bedirectly cooled using a cooling gas/air. The holders 62″ are preferablystiff enough to retain the preforms and have perforations or otheropenings 242 and 244 where the holders do not have any direct contactwith the preforms. By having these kind of holders that only partiallycover the outer surface of the preforms, the preforms can be cooled ontheir outer surfaces, while they are additionally cooled internally bythe cooling pins 74. In this case, the cooling step comprises thetransfer of the preforms from the mold to the take-off plate 60″, themovement of the take-off plate 60″ outside the molding area, to thecooling area which is adjacent the molding area. At the cooling area,the preforms 48 are internally cooled using the frame 98 and the coolingpins 74 that enter at least partially inside the preforms. At the sametime, the preforms 48 retained by the take-off plate 60″ have theirexterior surfaces convectively cooled by an additional cooling station250 that blows a coolant fluid towards the preform holders. As shown inFIG. 16, the additional cooling station 250 has a plurality of nozzles252, 254, and 256 for blowing coolant toward the outer surfaces of thepreforms. The nozzles 252, 254, and 256 blow cooling fluid throughwindows 258 in the take-off plate 60″ and onto the outer surface of thepreforms via windows or openings 242 and 244 in the preform holders. Thenozzles 252, 254 and 256 blow cooling fluid through openings 242 and 244in the preform holders 62″ and onto the outer surface of the preforms.While the additional cooling station 250 has been shown as havingnozzles for cooling two preforms, it should be recognized that inactuality the cooling station 250 may have as many nozzles as needed tocool the outer surfaces of any desired number of preforms.

The use of the additional cooling station 250 allows the preforms 48 tobe simultaneously cooled inside and out using cooling means that areindependent from the take-off plate 60″. This approach makes thetake-off plate 60″ very light, very fast and easy to service. Ifdesired, the preform holders 62″ may grip the preforms solely around theneck portion, thus leaving a more open window for the blown coolingfluid to cool the outer portion of the preforms.

According to another embodiment of the invention, the take-off plate mayinclude external cooling means using blown air or may include no coolingmeans. In both cases, internal cooling is achieved using the novelcooling method and apparatus of the present invention.

The innovative cooling method and apparatus of the present invention areextremely beneficial for cooling preforms molded in high cavitationmolds. It is well known that the temperature of the molten resin flowingthrough a mold varies quite substantially for a various of reasonsincluding: (a) non-uniform heating of the hot runner manifold; (b)formation of boundary layers inside the manifold's melt channels; (c)non-uniform mold cavity cooling; and (d) insufficient cooling at themold gate area. One consequence of the temperature variations across themold is that the cooling time has to be adjusted at the local level sothat the hottest preforms are cooled before any crystallinity occurs inthe final preforms. In order to prevent formation of crystallized zones,the cooling system of the present invention is able to provide adifferent cooling pattern that can be tuned according to the temperaturesignature of each mold. Sensors in the take off plate 60 can be providedto regulate the amount of cooling from each cooling pin 74. Anotherconsequence of the non-uniform temperature inside the mold is that inmost cases the gate sprue area located on the dome section 22 of thepreforms is the hottest part of the molded preform. Because this spruegate portion is slower cooled in the mold closed position, chances arethat this portion will be highly crystalline if the in-mold cooling istoo long or if no additional cooling is provided outside the mold.According to the present invention, the cooling pins 74 blowing cold airinside the preform immediately adjacent the sprue gate area is a noveloperation that prevents in a very efficient manner the formation ofcrystallized areas in the preform.

The innovative cooling method and apparatus of the present invention arealso beneficial for compensating for the cooling inefficiency of thetake-off plate. It may happen that due to the imperfect contact betweenthe hot molded article and the cooling tube, the temperature of themolded article held by the take-off plate may vary across the plate.According to the present invention, the temperature sensors located inthe take-off plate or the cooling frame can be used to provideinformation to a cooling control unit that varies the amount of coolingfluid directed to each preform.

The adaptive cooling approach mentioned so far is also beneficialbecause it can take into account the fact that the temperature patternof the molded preforms can vary during the day, the function of thespecific resin used, the function of the machine settings, or due tolocal variations in the thickness of the preforms caused by impropervalve stem actuation in the hot runner nozzle or due to uneven coreshift in the mold cavities. These situations are neither predictable noreasy to fix; however, the present invention provides a mechanism to tunethe post-molding cooling step for each cavity based on the temperatureof each molded article or preform.

A significant reduction of the cycle time for the benefit of increasingthe post molding cooling time can be achieved by simplifying the designand the movements of the take-off plate and the cooling frame. This hasto take into account very critical assembling, servicing and operationconstraints such as rigidity, movement accuracy, alignment between thecooling pins and the molded articles or preforms on the take-off-plateand vibrations. Also the location of the cooling frame with the pins hasto be decided in such a manner to reduce the “foot print” of the entiremachine.

Reference is made in this regard to FIGS. 13(a) and 13(b) which showanother embodiment of the present invention where the take-off plate 60remains in a vertical position during the additional air cooling step,i.e. parallel to the mold plates 32, 26. The cooling frame 98 istranslated towards the take-off plate 60 and the cooling pins 74 enterthe molded articles or preforms 48. After all the preforms are cooled,the cooling frame 98 is retracted, the take-off plate 60 is rotated at90° and parallel to a conveyor 114 and then the cooled preforms areremoved from the plate 60. This approach simplifies the design of thecooling frame which does not need rotation means and means to preventits interference with the preforms ejected from the plate.

Further reference is made to FIG. 14 which shows another embodiment ofthe invention where the robot take-off plate 60 comprises additionaltranslation means 150 to move the performs 48 along an axis parallel totheir axis of revolution. This additional movement of the preforms 48simplifies the cooling frame 98 which remains substantially stationaryduring the cooling process. As shown in FIG. 14, the take-off plate 60or other means for holding the performs is translated along the axis Xtowards the stationary cooling frame 98. After the cooling step, thetake-off plate 60 is rotated by 90° so that it faces the conveyor 114and thus the cooled preforms are ejected.

Further reference is made to FIG. 15 which shows novel air cooling meansattached to the take-off-plate 60. The approach shown in this figureeliminates the need for a separate frame for holding the cooling pinsand thus reduces the size of the cooling system and thus of theinjection molding machine. The new cooling pins 174 have an approximateU-shape and can be moved all together parallel to the preforms 48 sothat they can be introduced inside the preforms and moved out of thepreforms using a thin strip 176 actuated by piston BB or any other knownmeans. The pins 174 can be also rotated around an axis “A” parallel tothe preform so that they can be brought into or removed from axialalignment with the preforms. This simultaneous rotation of all the pins174 can be achieved using any suitable means known in the art. Accordingto the invention, the U-shaped cooling pins 174 have an ARM “A” thatenters the preform, an ARM “C” parallel to ARM “A” that is used formoving ARM “A”, and an ARM “B” that connects ARM “A” to ARM “C”. Therotation of the pins around the axis A of ARM “C” can be done in variousways. As shown in FIG. 15, this can be done using an elongated rack 178,operated by piston AA, that is in engagement with pinions 180 attachedto the ARM “C” of each cooling pin. The same rotation can be done usingfrictional means, one in translation and the other in rotation. Duringthe transfer of the preforms 48 from the cores 38 to the cooling tubes62 of the take off plate 60, the U-shaped cooling pins 174 can be“parked” in a dedicated location located adjacent each cooling tube 62,so that they do not interfere with the moving preforms and less space isneeded to open the mold. Immediately after the preforms 98 are retainedin the take-off plate 60, the cooling pins 174 attached to the plate 60are moved forward by the piston BB and the strip 176 and when they reacha certain height which allows ARM “A” to be on top of the preform, theyare rotated in axial alignment with the preforms and finally introducedinside the preforms through the retreat of the piston BB. The permanentcontact between the strip 176 and each ARM “C” is provided by a coilspring 182 which operates against shoulder 181 or any other appropriatemeans. A flexible tube 184 is used to supply blowing air to each coolingpin through ARM “C”. This design of the cooling pins attached to thetake-off plate brings the following advantages: simplifies and reducesthe size of the cooling system, improves the cooling rate because insidecooling starts immediately after the preforms are in the take-off plate,inside cooling can be done during the movement of the take-off plate andpractically continuously for as long as the preforms are also cooled bythe take-off plate. During the ejection of the cooled preforms, thecooling pins must be again rotated towards their initial position sothat they are no longer aligned with the preforms.

Further reference is made to FIG. 12 which shows air cooling meanscomprising cooling channels 210 incorporated in the mold halves 32, 36that allow cooling of the preforms held by the mold cores, during andimmediately after opening the mold and before the take-off plate entersthe molding area. This additional cooling step will further solidify thepreform before the take-off plate is brought into the mold area andbefore they are transferred to the take-off plate.

According to another embodiment of the present invention, that can beeasily understood from other drawings in this application, the robot andthe take-off plate retain only a single batch of preforms. After theinjection steps, the take-off plate is parked outside the mold area andcooling air or refrigerated air is blown inside each preform from thecooling pins. The cooled preforms are ejected form the take-off platethat will be brought back into the molding area without carrying anypreforms.

FIG. 23 illustrates an alternative construction of the frame 98 forholding the cooling pins 74. As shown in this figure, the frame 98 mayhave cooling pins 74 on two opposed surfaces. Further, the frame mayrotate about a first axis 300 and a second axis 302 which isperpendicular to the first axis 300. Any suitable means (not shown)known in the art may be used to rotate the frame 98 about the axes 300and 302.

By providing this type of construction, it is possible to have a firstset of cooling pins 74 engage the preforms 48 in a take-off plate 60 andbegin internal cooling of the preforms. The preforms 48 may then betransferred out of the holders 62 in the take-off plate 60 onto the pins74. The frame 98 can then be rotated about one or more of the axes 300and 302, while internal cooling of the preforms 48 is being carried outby the pins 74. After the first set of preforms has reached theleft-hand position shown in FIG. 23, a second set of cooling pins 74 mayengage a second set of preforms 48 held in the take-off plate 60. Ifdesired, the left-hand set of preforms 48 can have their exteriorsurfaces convectively cooled using a cooling station 304 having aplurality of nozzles (not shown) for blowing cold air onto the exteriorsurfaces. If desired, the frame 98 may have a preform retaining plate308 attached to it.

It is apparent that there has been provided in accordance with thepresent invention a preform post-mold cooling method and apparatus whichfully satisfies the means, objects, and advantages set forthhereinbefore. It is evident that many alternatives, modifications, andvariations will be apparent to those skilled in the art in light of theforegoing description. Accordingly, it is intended to embrace all suchalternatives, modifications, and variations as fall within the spiritand broad scope of the appended claims.

1. Apparatus for cooling a molded article made in an injection moldformed from mold halves, the molded article having a first region at arelatively high heat and an adjacent region at a relatively lower heat,the apparatus comprising: an end-of-arm tool having at least one holder,the end-of-arm tool being configured to be movable between (i) a firstposition between the mold halves where it receives the molded articleinto a respective one of the at least one holder, and (ii) a secondposition outside of the mold, the at least one holder being configuredto hold a molded article at a time when the molded article retains anamount of heat; and a cooling pin on a frame located adjacent the secondposition, the cooling pin having a tip, said frame being configured tomove relative to the end-of-arm tool to cause insertion of the tip ofthe cooling pin into the molded article after the end-of-arm toolreaches the second position; said cooling pin having an internal channelterminating at the tip, said frame and said cooling pin being configuredto cause the cooling pin, upon insertion into the molded article byrelative movement of the frame and the end-of-arm tool, to be within themolded article but spaced away from the first region and not in contacttherewith, said cooling pin being configured to be connectable to acooling fluid delivery system arranged to force gaseous cooling fluidalong the internal channel to cause expulsion of the gaseous coolingfluid from the tip mostly in a direction of the first region toaccentuate cooling within at least the first region; said frame beingconfigured to be positioned, during the expulsion of the gaseous coolingfluid from the tip, with respect to the end-of-arm tool such as todefine an open system having a passageway allowing venting of gaseouscooling fluid from an interior of the molded article to an ambientenvironment; and said apparatus being configured to be operational,during the expulsion of gaseous cooling fluid from the tip, to distancethe frame from the end-of-arm tool, and the passageway of the opensystem is produced by formation of a space between a region of anexternal surface of the cooling pin and an open end of the moldedarticle both located within the respective holder.
 2. Apparatusaccording to claim 1, wherein the apparatus is configured to introducethe tip of the cooling pin into the preform to a depth that allows thecoolant to reach and cool an internal dome portion of a preform. 3.Apparatus according to claim 1, wherein the frame positions the coolingpin within the molded article such that: i) the tip is displaced a firstdistance (d) from the first region of the molded article; ii) a sidewallof said cooling pin is located a second distance (D) from internalsidewalls of the molded article; and a ratio of the first distance tothe second distance (d:D) is in the range of about 1:1 to about 10:1. 4.Apparatus according to claim 1, wherein the gaseous cooling fluidcomprises cooled pressurized air that is blown along the internalchannel.
 5. Apparatus according to claim 4, further including a valvefor supplying regulated amounts of gaseous cooling fluid to the coolingpin.
 6. Apparatus according to claim 1, wherein the tip has one of adivergent nozzle construction and a straight-walled nozzle construction,and wherein the internal channel and tip, when located within the moldedarticle, focus the gaseous cooling fluid towards a region principallysurrounding a first region.
 7. Apparatus according to claim 1, whereinthe cooling pin has one of: i) a varying diameter along its length; ii)lateral fluid outlets or radial conduits in the sides of the coolingpin, the lateral outlets or radial conduits coupled to the internalchannel and arranged to direct cooling fluid to at least one of a neckportion and a body portion of the molded article; iii) grooves along anexterior surface of the cooling pin; iv) ribs spaced about the peripheryof the cooling pin, the ribs protruding from the cooling pin to reduce,in use, over a length of each rib a dimensional separation of anexterior surface of the cooling pin to the internal wall of the moldedarticle; and v) a plurality of contact elements along an exteriorsurface of the cooling pin.
 8. Apparatus according to claim 1, wherein:the end-of-arm tool supports a plurality of holders; and the frameincludes fewer cooling pins than there are holders on the end-of-armtool; whereby, in use, only selected ones of the molded articles inrespective holders are cooled by aligned insertion of a tip of a coolingpin into each selected one of the molded articles.
 9. Apparatusaccording to claim 1, further comprising: a suction device selectablyconnectable to the cooling pin, the suction device being operational, inuse, after cooling of the molded article by expulsion of the gaseouscooling fluid from the tip, to extract the molded article from itsrespective holder by drawing the molded article towards the tip underreduced pressure.